Do a search on evaporator replacements for a 140 chassis as this has been covered a lot in the past. This is a common failure on 124 and 140s and now some MLs are also failing.
The 140 is about a 21.8 hour labor and $700 evaporator cost not including a new drier and expansion valve while in there. The 140 from 92 onwards to around 95 were very troublesome in many ways...the reason I unloaded mine!